Conventionally, an image forming apparatus takes out a paper in a paper feed cassette through a pickup roller. Further, the paper taken out from the paper feed cassette is guided to a transfer roller through a register roller. To align the positions of the paper and a toner image to be formed on a photoconductive drum, the register roller rotates at given timing, and conveys the paper to a transfer position. The paper passing through the transfer roller is conveyed to a fixing device.
Further, a conveyance roller is arranged at the upstream side of the register roller. The front end of the paper conveyed by the conveyance roller is abutted against the register roller. If the front end of the paper is abutted against the register roller, the paper is bent, thus correcting the skew of the front end of paper.
Incidentally, if the paper to be conveyed is a thin paper, the stretching force of the paper when the paper is bent is small. However, if the paper is a thick paper, since the rigidity of the paper is strong, the stretching force is large. If the stretching force of the paper is large, a returning force that enables the conveyance roller to rotate backward occurs.
At this time, if the idling load of the conveyance roller is stronger than the returning force of the paper, the conveyance roller doesn't rotate backward. However, if the idling load of the conveyance roller is weaker than the returning force of the paper, the idling load is lost to the returning force of the paper, and thus the conveyance roller rotates backward. If the conveyance roller rotates backward, the front end of the paper separates from a nip of the register roller. Thus, the positions of the front end of papers are scattered, which leads to a conveyance failure such as an occurrence of a skew and the like.